"To come out and say, major changes of projects and it's only going to cost $85 million should send alarms bells to South Australians," she said.

But Mr Mullighan said the rail project was not a pipedream.

"I don't think it is, it's a relatively modest investment, particularly if we are sharing the cost with the Federal Government," he said.

Road project consultation also criticised

Mitcham Mayor Glenn Spear was also disappointed with the State Government's lack of consultation.

He said council staff should have been consulted over yesterday's South Road upgrade announcement at Darlington.

"For 12 months that I have been Mayor, I have been attending the various briefing sessions held on the South Road project and we were given barely a day's notice and I wasn't happy about that," he said.

"I thought it was very unfair, I haven't seen any detail of the project, nor have any of the Mitcham staff."

The Government plans to extend the South Road upgrade at Darlington by one kilometre, which it said would come at no extra expense to taxpayers.

Mr Mullighan said the extra kilometre would pass through the Ayliffes Road intersection, making travel times shorter for drivers once the project is complete.

Construction on the Darlington project is expected to start in early 2016, and to be completed by the end of 2018.

The Darlington upgrade project is being jointly funded with $496 million from the Federal Government and $124 million from the South Australian Government.

The Darlington interchange project is part of the broader $2.5 billion North-South corridor upgrade.

The Federal Government has committed $1.7 billion to the project over the next 10 years.

The State Government wants South Australian workers to make up 90 per cent of the workforce on the project, and 50 per cent of those workers to be from the southern suburbs.